Background: With the recent growth of interest in cell-based therapies and radiolabeled cell products, there is a need to develop more robust cell labeling and imaging methods for in vivo tracking of living cells. This study describes evaluation of a novel cell labeling approach with the positron emission tomography (PET) isotope <sup>89</sup>Zr (T<inf>1/2</inf> = 78.4 h). <sup>89</sup>Zr may allow PET imaging measurements for several weeks and take advantage of the high sensitivity of PET imaging. Methods: A novel cell labeling agent, <sup>89</sup>Zr-desferrioxamine-NCS (<sup>89</sup>Zr-DBN), was synthesized. Mouse-derived melanoma cells (mMCs), dendritic cells (mDCs), and human mesenchymal stem cells (hMSCs) were covalently labeled with <sup>89</sup>Zr-DBN via the reaction between the NCS group on <sup>89</sup>Zr-DBN and primary amine groups present on cell surface membrane protein. The stability of the label on the cell was tested by cell efflux studies for 7 days. The effect of labeling on cellular viability was tested by proliferation, trypan blue, and cytotoxicity/apoptosis assays. The stability of label was also studied in in vivo mouse models by serial PET scans and ex vivo biodistribution following intravenous and intramyocardial injection of <sup>89</sup>Zr-labeled hMSCs. For comparison, imaging experiments were performed after intravenous injections of <sup>89</sup>Zr hydrogen phosphate (<sup>89</sup>Zr(HPO<inf>4</inf>)<inf>2</inf>). Results: The labeling agent, <sup>89</sup>Zr-DBN, was prepared in 55% ± 5% decay-corrected radiochemical yield measured by silica gel iTLC. The cell labeling efficiency was 30% to 50% after 30 min labeling depending on cell type. Radioactivity concentrations of labeled cells of up to 0.5 MBq/10<sup>6</sup> cells were achieved without a negative effect on cellular viability. Cell efflux studies showed high stability of the radiolabel out to 7 days. Myocardially delivered <sup>89</sup>Zr-labeled hMSCs showed retention in the myocardium, as well as redistribution to the lung, liver, and bone. Intravenously administered <sup>89</sup>Zr-labeled hMSCs also distributed primarily to the lung, liver, and bone, whereas intravenous <sup>89</sup>Zr(HPO<inf>4</inf>)<inf>2</inf> distributed to the liver and bone with no activity in the lung. Thus, the in vivo stability of the radiolabel on the hMSCs was evidenced. Conclusions: We have developed a robust, general, and biostable <sup>89</sup>Zr-DBN-based cell labeling strategy with promise for wide applications of PET-based non-invasive in vivo cell trafficking.
- Cell labeling
- In vivo cell tracking
- Zirconium-89, PET
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging